It is known in the art that optically active diphosphinites derived from carbohydrates can be used as ligands for the metals Rh and Pt in the asymmetric hydroformylation of vinyl arenes. The major problem that has plagued the well-known Pt-catalyzed hydroformylations, however, is the unfavorable branched to linear ratios which reduce overall selectivity. The Rh-catalyzed reactions generally give good branched to linear ratios but enantioselectivity is poor. A series of metal/ligand combinations which overcome these limitations is the subject of this application.
Ojima, I. and Hirai, K., "Asymmetric Hydrosilylation and Hydrocarbonylation" in Asymmetric Synthesis; Morrison, J. D., Ed.; Academic Press, Orlando, Fla., 1985; pp 103-146 and Jackson, W. R. and Lovel, C. G., Aust. J. Chem., 35, 2069-75 (1982) describe low asymmetric induction in the hydroformylation of vinyl acetate in the presence of a phosphinite derived from tartaric acid.
German patents DD280,473, DD275,623 and DD275,671 and references Selke et al., J. Mol. Cat., 37, 213-225 (1986) and Selke, J. Organometal. Chem., 370, 249-256 (1989) disclose related rhodium carbohydrate catalysts mainly for enantioselective hydrogenation reactions, but no teaching is provided which demonstrates or enables effective enantioselective hydroformylation, and the importance of electronic effects of these ligands is not suggested.
Ligands similar to those used in the present invention are disclosed in RajanBabu, T. V. and Casalnuovo, A. L., J. Am. Chem. Soc., 114, 6265-6266 (1992) and U.S. Pat. No. 5,175,335, for use in other catalyst compositions for asymmetric hydrocyanation.
High enatioselectivities are most often explained on the basis of steric arguments, see for example, Brown, J. M., Chem. Soc. Rev., 25 (1993), and references cited therein. For a recent example of the application of classical and widely used steric approach to design of enantioselective catalysts see: Trost, B. M. et al. J. Am. Chem. Soc. 114, 9327 (1992) and references cited therein. Recently, electronic effects are described as being effective in enhancing enantioselectivity in manganese-catalyzed oxidation, Jacobsen, E. N. et al., J. Am. Chem. Soc. 113, 6703, (1991), and in nickel-catalyzed hydrocyanations, RajanBabu, T. V. and Casalnuovo, A. L., J. Am. Chem. Soc., 114, 6265-6266 (1992). No teaching of electronic effects in the enantioselective hydroformylation reaction have been described.